Interpretive Summary: Reproduction in many finfish is coordinated through the release of hormones via the endocrine system. Hormones can also be released into the water as pheromones and serve as an avenue of communication to alter the reproductive state of the opposite sex. Pheromones are typically detected by special cells within the nose of the animal and result in a cascade of events within the brain and reproductive organs to prepare the animal for spawning. The goldfish provides an excellent model for understanding pheromonal communication because the system has been studied in this species with a high level of sophistication for several decades. In this study, we evaluated the specific effects of the two goldfish pheromones, prostaglandin F2a (PGF2a) and 17a, 20ß-dihydroxy-4-pregnen-3-one (17, 20ß-P). It had been previously shown that these two pheromones were able to stimulate different sets of olfactory receptor neurons in the brain, suggesting each compound mediates a different physiological response in fish. We therefore examined the effects of these two pheromones on the behavior, brain function and release of plasma hormones in the goldfish. Our results suggest that PGF2a elicits behavioral changes that are accompanied by alterations in brain function in male goldfish. On the other hand, exposure to 17, 20ß-P increased plasma levels of the steroid androstenedione (AD) in males; and in females it increased mRNA levels of the androgen receptor and the gonadotropin-releasing hormone in the cerebellum. These results demonstrate the two pheromones, PGF2a and 17, 20ß-P, act through distinct molecular pathways and produce different neuroendocrine and behavioral responses in goldfish. This is the first finding that links a specific pheromone molecule (PGF2a) to generation of new nerve cells in a vertebrate animal. This study also impacts the agricultural community by increasing our degree of understanding on pheromonal communication in fish and has the potential to influence a number of practices in aquaculture that may enable better control of the reproductive cycle, including out-of-season, synchronized, and induced spawning.

Technical Abstract:
Goldfish (Carassius auratus) use reproductive hormones as endocrine signals to synchronize sexual behavior with gamete maturation, and as exogenous signals (pheromones) to mediate spawning interactions between conspecifics. We examined the differential effects of two hormonal pheromones, prostaglandin F2a (PGF2a) and 17a, 20ß-dihydroxy-4-pregnen-3-one (17, 20ß-P), which had been known to stimulate different sets of olfactory receptor neurons, on neurogenesis, neurotransmission and neuronal activities, and on plasma androstenedione (AD) levels. Exposure to waterborne PGF2a induced a multitude of changes in male goldfish brain. Histological examination indicated an increase in the number of dividing cells in male diencephalon (p < 0.05, Kruskal-Wallis Test). Real-time quantitative PCR tests showed elevated levels of transcripts for the salmon GnRH in the male telencephalon and cerebellum (p < 0.005, One-Way ANOVA), and for choline acetyltransferase (ChAT) in the male vagal lobe and the brain stem underneath the vagal lobe (p < 0.05, One-Way ANOVA). Therefore, PGF2a seemed to modulate male brain plasticity associated with behavioral changes during spawning season. Exposure to waterborne 17, 20ß-P, on the other hand, increased circulatory levels of immunoreactive AD in males and the transcripts of androgen receptor and chicken-II GnRH (cGnRH-II) in the female cerebellum (p < 0.05, One-Way ANOVA). PGF2a and 17, 20ß-P thereby seemed to act through distinct pathways to elicit different responses in the neuroendocrine system.